This application claims priority from Korean Patent Application No. 2003-28171, filed on May 2, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the invention
The present invention relates to an electrophotographic image forming apparatus. More particularly, the present invention relates to a method of controlling an amount of toner charging in an electrophotographic image forming apparatus using a two-component developing agent.
2. Description of the Related Art
In general, an electrophotographic image forming apparatus is a device which develops an electrostatic latent image formed on a photosensitive body using a developing agent, forms a toner image, and then, transfers and fuses the toner image onto a recording medium, thereby printing an image.
A two-component developing agent typically comprises toner representing a predetermined color, and a carrier for transferring toner from a developing unit to the photosensitive body More specifically, in case of a nonmagnetic two-component developing agent, the toner is charged, attached to the carrier due to an electrostatic force, and transferred to the photosensitive body. The toner is mixed with the carrier and agitated in the developing unit, and then charged due to friction with the carrier.
Parameters that affect the amount of toner charging include the ratio of the carrier and the toner, an agitation time, and the amount of developing agent. As the speed of the electrophotographic image forming apparatus increases, the agitation time has a greater affect on the amount of toner charging.
In particular, when an image having a low concentration of imaging, such as about 1–2% or a substantially white image is printed, the amount of toner developed on the photosensitive body is small. Thus, new toner is not supplied to an agitation region in which the toner and the carrier are agitated. If the toner is continuously agitated with the carrier in this state, the toner becomes overcharged. As a result, an attaching force between the toner and the carrier becomes excessively large, and the toner is not well developed on the photosensitive body when a next image is printed and the carrier is also developed on the photosensitive body, thereby lowering the concentration of toner on the formed image.